ANNAPOLIS, Md. – Wiping away tears, Sen. John McCain’s message for the Naval Academy’s midshipmen was rooted in the spirit of service.

But the Arizona Republican had a not-too-veiled message for the current commander in chief.

“We have to fight against propaganda and crackpot conspiracy theories. We have to fight isolationism, protectionism, and nativism. We have to defeat those who would worsen our divisions,” McCain said. “We have to remind our sons and daughters that we became the most powerful nation on earth by tearing down walls, not building them.”

That particular line generated applause among the young men and women in uniform who had filled the alumni hall for the lecture. The message had echoes of the remarks McCain delivered two weeks ago in Philadelphia, accepting an award from the National Constitution Center.

[Photos: 50 Years After Plane Shot Down, McCain Addresses Naval Academy]

There, he warned of “half-baked, spurious nationalism,” but the tone here was different, perhaps owing to the younger audience.

Fighting that battle, he said, “isn’t your job. Not directly.”

“It belongs to those of us who hold office and are responsible for making sure you’re sent where you’re needed and equipped and ready for your missions,” the chairman of the Senate Armed Services Committee said.

During a Q&A session with the midshipmen that McCain repeatedly extended despite the fact that the event, with its to-the-minute military precision, was already running late, he faced a question about the news of the day and Russian meddling in the 2016 presidential election.

“I’ve seen these scandals before, and it’s a centipede. Every few days, another shoe drops, and so the latest news today of these indictments, I could have predicted these months ago,” McCain said of the indictments of onetime Trump campaign aides Paul Manafort and Rick Gates.

The senator said he was not offering career advice, but he was clearly encouraging the students to become involved in cybersecurity.

“I’m very worried about the erosion of confidence of the American people in the election system, because if we lose confidence in the results of our elections — that we don’t believe them — that attacks the very fundamentals of what America was all about and was founded on,” McCain said.

“We have to make sure that we get into this business of cyberwarfare,” he added, a likely allusion to the Russian election interference.

McCain also offered a history lesson featuring a fairly direct analogy between nationalist isolationism and the rise of fascism after World War I.

“The American example and American leadership are indispensable to securing a peaceful and prosperous future. Our failure to remain engaged in Europe and enforce the hard-won peace of 1918 had made that clear,” he said. “There could be no more isolationism, no more tired resignation — no more ‘America First,’” he said, a swipe at President Donald Trump’s unapologetic recycle slogan. 

“We are asleep in our echo chambers, where our views are always affirmed and information that contradicts them is always fake. We are asleep in our polarized politics, which exaggerates our differences, looks for scapegoats instead of answers, and insists we get all our way all the time from a system of government based on compromise, principled cooperation and restraint,” he said. “It’s time to wake up.”

McCain’s Monday visit to the Naval Academy came less than a week after the 50th anniversary of his plane being shot down over Vietnam and being taken a prisoner of war.

Former Virginia Republican Sen. John W. Warner, who served as chairman of the Armed Services Committee as well as secretary of the Navy, introduced his former colleague.

Warner said he first met McCain while serving as Navy secretary when the current senator came home after being a prisoner of war.

“Vietnam was on our mind, morning, noon and night,” Warner said, adding that the status of POWs like McCain had been on the top of the agenda of his intelligence briefings during the war.

“That’s where I first began to learn about John and his dedication to this country,” he said.

Warner called the invitation to participate in the ceremony Monday a “very important moment in my life.”

“You’re here because you want to defend our country and you want to defend freedom all over the world,” he said.

“America must remain strong militarily. America must protect its values,” Warner added, drawing applause — with the retired lawmaker pushing for more. “Come on, you can do better than that.”

That McCain’s appearance came just as Defense Secretary James Mattis and Secretary of State Rex Tillerson had finished testifying on the Trump administration’s views regarding authorizations for use of military force, there was an unavoidable reality.

Just as McCain had gone to Vietnam after graduating from this place, the young men and women listening to and asking questions of the Arizona senator on Monday night will be the ones fighting the nation’s current wars and next war — wherever they may be.

The speech came almost 60 years since the senator was a midshipman himself. 

As he often does, McCain made light of his mediocre academic performance. But he spoke candidly about the lessons of his time at the academy, as well as what he learned after receiving his commission.

“I wanted to be a fighter pilot. I wanted to shoot down airplanes,” McCain said. “I didn’t give a s— what else I wanted to be.”

“When you go to a squadron, and you’re 16 pilots and 12 airplanes, you get responsibilities. You get responsibilities for the men and women who are in your squadron,” McCain said.

His address the Brigade of Midshipmen marked his first appearance on campus since 2012, and perhaps his last.